Infra red (IR) spectroscopy is used to perform qualitative and quantitative analysis of materials based on the transmission of a light beam through a sample such that different frequency components of the light beam are absorbed by different components of the sample, whereby a frequency analysis of the light emerging from the sample permits analysis of the sample itself.
At its most basic, a spectrophotometer comprises at least the following components: a light source for producing a beam of light, a sample positioned in the path of the light beam and a detector. Since, in practice, the light source is not a point source but, rather, emanates over a relatively broad area, the light beam has a non-uniform cross-section. Consequently, the light passing through a particular portion of the sample depends on the position of the light source relative to the sample and any relative movement therebetween produces different results.
A further consideration which can lead to erroneous results relates to the uniformity of the sample itself. Since this, too, may be non-uniform, even if an ideal light source were employed having a completely uniform cross-section, the detector on the far side of the sample may sense a portion of the light which is not representative of the complete sample owing to the non-uniformity of the sample itself.
These problems may, to some extent, be solved by inserting a diffuser in the light path, but this results also in a loss of light energy and a smaller detector signal.